The spectroscopic properties of Ni²⁺ ions are particularly intriguing due to their emission in the near-infrared (NIR) range, which enables various potential applications [1]. One notable potential application of the luminescence of Ni²⁺ ions is pressure sensing, due to the dependence of the energy of the ³T₂g level on the strength of the crystal field, which is altered by pressure-induced changes in the metal--oxygen distances [2]. Consequently, applying pressure should affect the spectroscopic properties of Ni²⁺ ions. To explore the potential of Ni²⁺ ions as luminescent manometers, we investigated the luminescence of Ni²⁺ ions in doped spinel-type gallate under applied hydrostatic pressure. The change in energy of the ³T₂g excited state of Ni2+ caused by the change in crystal field strength resulted in a significant spectral shift of the emission band associated with the ³T₂g→³A₂g electronic transition of Ni²⁺ ions, exceeding 10 nm GPa⁻¹. Based on this substantial shift, we proposed a ratiometric readout mode using the luminescence intensity ratio (LIR), defined by integrated two spectral ranges of the broad emission band of Ni²⁺ ions. This approach, which is uncommon for luminescence manometry, offers exceptional high-pressure sensitivity of more than 50% GPa⁻¹, while also ensuring temperature-independent pressure readouts. Our results demonstrate the significant potential of both the ratiometric approach and the utilization of Ni²⁺ ions for optical pressure sensing applications.
Acknowledgement: This work was supported by the National Science Center Poland (NCN) under project No. 2023/49/N/ST5/01020.
[1] C. Matuszewska et al., Journal of Luminescence 2020, 223, 117221
[2] M.G. Brik et al., Journal of Luminescence 2014, 148, 338-341
